In the related art, a turbocharger which compresses air of an internal combustion engine and feeds air having high density to a combustion chamber is known, and for example, the turbocharger is widely used in a two-stroke low-speed engine such as a marine diesel engine or a diesel engine for generating power. In the turbocharger, a compressor which compresses combustion air and a turbine serving as a drive source of the compressor are coaxially connected to each other, and the compressor and the turbine are accommodated in a casing and are integrally rotated. In addition, the turbocharger turbine is driven by energy held in exhaust gas of an internal combustion engine.
As the above-described turbocharger, a hybrid turbocharger in which a high-speed motor generator is connected to a rotor shaft is known. Similarly to a general turbocharger, the hybrid turbocharger can supply pressurized combustion air to an internal combustion engine and generate electricity using excess exhaust gas energy to supply power. In addition, when a motor generator of a hybrid turbocharger is installed inside a silencer of a compressor side, in general, the hybrid turbocharger has a size capable of approximately penetrating the silencer.
In addition, an electric assist turbocharger is known, in which a miniaturized motor is adopted instead of the motor generator of the above-described hybrid turbocharger and the motor is housed in the turbocharger. In the electric assist turbocharger, the miniaturized motor is attached to a shaft extension portion in which a rotor shaft extends in an inlet air passage side. In this case, since a size of the motor is small, it is possible to sufficiently support a weight of the motor rotor by the existing bearings of the turbocharger. Accordingly, in general, a structure in which a dedicated bearing for a motor is not required, that is, a motor overhang structure which does not have a dedicated bearing for a motor is adopted. In the electric assist turbocharger, for example, when a sufficient amount of exhaust gas cannot be obtained during a low load of a main engine, the motor is used to assist turbocharger's compression by consuming electricity to supply enough scavenging pressure to the main engine in place of an auxiliary blower.
Moreover, Japanese Unexamined Patent Application Publication No. 2013-24059, for example, discloses an electric supercharging compressor including rolling bearings which are provided on both sides of an electric motor and support a rotary shaft, and an assembly method thereof.